Well-defined triphenylamine-containing polymers as hole-transporting layers in solution-processable organic light-emitting diodes via living anionic polymerization

Abstract

In this study, we conducted anionic polymerization of N-[1,1′-biphenyl]-4-yl-N-(4′-ethenyl[1,1′-biphenyl]-4-yl)-9,9-dimethyl-9H-fluoren-2-amine (A) incorporating a triphenylamine group as a hole-transporting unit using sec-butyllithium and potassium naphthalenide as initiators in tetrahydrofuran at −30 ℃ for 10 min. The resultant poly(A)s exhibited controlled molecular weights (Mn = 20.9−126.3 kg/mol) and narrow molecular weight distributions (Mw/Mn ≤ 1.12). The living nature of the propagating chain end of poly(A) was confirmed by postpolymerization. Additionally, block copolymerization of A with styrene (St) and 2-vinylpyridine (2VP) was performed to assess its relative reactivity. Copolymerization resulted in the precise synthesis of well-defined block copolymers with poly(A) segments. Thermal properties of poly(A) were investigated using thermogravimetric analysis and differential scanning calorimetry. Notably, the thermal annealing of poly(A) film at 230 ℃ for 10 min made it insoluble in toluene, indicating its solvent resistance. Thus, poly(A) was used as the hole-transporting layer (HTL) in solution-processable organic light-emitting diodes (OLEDs). A comparative analysis against a reference device containing poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) revealed an enhancement in the performance of the OLED comprising thermally annealed poly(A) as the HTL. These results strongly suggest that poly(A) is a promising HTL material for solution-processable OLEDs.